The invention is based on a control valve according to the preamble of claim 1.
A thermostatic valve is often used in cooling circuits of internal combustion engines for vehicles to control the temperature. This valve comprises a valve body that is controlled by an expansion actuator depending on coolant temperature and releases or closes a branch of flow to a heat exchanger and adjusts a bypass line accordingly in complementary fashion so that the optimal operating temperature of the internal combustion engine is reached as quickly as possible and is kept constant. Such thermostatic valves are sluggish due to the slowly-proceeding heat transfer to the expansion actuator.
DE 41 09 498 A1 makes known a device and a method for controlling the temperature of an internal combustion engine of a motor vehicle. The cooling circuit of the internal combustion engine comprises a heat exchanger that can be circumvented by a bypass line. To control the coolant flow, a control valve is provided in the outlet region of the bypass line, the position of which is set using a control unit by way of a control line, so that more or less coolant can be directed past the heat exchanger. To this end, the control device specifies a temperature setpoint that is determined as a function of various operating conditions and operating parameters of the internal combustion engine. The setpoint is compared with the actual value of the engine temperature and a position variable for the control valve is formed from the result. A cooling fan that is assigned to the heat exchanger is also controlled by the control device by way of a separate line.
DE 197 31 248 A1 makes known a control valve that adjusts the inflow of coolant of an internal combustion engine of a motor vehicle into the heat exchanger of a heating system. It has a slide switch as a shutoff element and, as the drive, a permanent magnet arranged on the slide switch, which permanent magnet is situated in sliding fashion in the magnetic field of a drive coil that can be acted upon with the signal current in the positioning direction of the slide switch. The control valve is moved in the opposite direction by means of a return spring, so that it is steplessly adjustable depending on the size of the respective signal current contacting the drive coil.
In the known control valves, the valve setting is not detected and returned to the control unit, so that the respective valve position is not known. Since the most exact understanding possible of the flow rates in the individual branches of the cooling system is required for good control behavior of the entire thermomanagement, however, additional flow rate sensors are to be provided.
DE 3200457 C2 makes known a method and a device for controlling an electromagnetic setting element. In this method, the position of a valve is detected and taken into account in the control. The actual value and the setpoint of the control loop are brought together at a summation point, and the system deviation is sent to a PI amplification arrangement. Its output signal controls a pulse-duration modulator by way of a rectifier arrangement, by way of the output signals of which a voltage ramp generator can be switched on. The ramp signal is sent to two voltage-current converters, by way of which a corresponding current ramp is generated that acts upon two electromagnetic setting elements. The two electromagnetic setting elements can be solenoid valves, for example, by way of which a pneumatic or hydraulic pressure increase or decrease is controlled or regulated in a further setting element, whereby its position, as an actual value, can, in turn, be sent to the summation point.
EP 0 665 381 B1 makes known a hydraulically actuated armature having an electric drive motor, a pump, and a hydraulic switch a so-called compact unit. This can be a valve, for example, that is acted upon on both sides by pressure. A directional control of the valve is carried out by way of the reversal of the direction of rotation of the drive motor that drives the pump, which is situated inside the compact unit between the two connecting lines of the valve. As a result, the pump supplies the connecting lines with hydraulic fluid, depending on the direction of rotation. The drive motor is thereby controlled electrically by a central control unit. Located in the end positions of the valve setting element are limit switches that emit a signal that, on the one hand, interrupts the assigned electric conductor for the drive motor and, on the other, activates a control element of the central control unit. According to a further embodiment, the drive motors are controlled by means of a bus system, whereby the end positions are also detected by limit switches. For an application in a thermomanagement system it is much too inexact to detect only the end positions.
According to the invention, the control unit of a control circuit generates a setpoint for the position of a valve member driven via electric motor or electromagnetically, which is processed by a second electronic control unit integrated in the control valve preferably in the form of a microcontroller with a determined actual value of the position of a valve member to a position variable for the position of the valve member.
The control valve according to the invention is located in a master control circuit having a first control unit, such as a cooling circuit of an internal combustion engine. The second control unit, together with the control valve, forms a lower-level control circuit. The control valve therefore receives an inherent control intelligence and can take on these important functions in case of failure even without the master first control unit.
According to an embodiment of the invention, the first or second control unit is equipped with failure detection that switches to emergency operation on its own in the case of failure. In the normal case, only a limited data exchange with the first control unit is necessary, so that control lines can be spared. The connection to the master control unit is used primarily to input the setpoint for the position of the valve member in the microcontroller of the control valve.
Advantageously, the microcontroller is programmable for different valve characteristics, so that, as part of a shared component strategy, as many of the same components as possible can be used in different controls. For example, control valves can be used in motor vehicles in a simple design without thermomanagement and in a higher-quality design with thermomanagement. The possibility therefore also exists to first use a control valve as a single module with the option of upgrading it later to thermomanagement with an additional control device. It is also feasible to combine multiple control valves with a communication line and to couple various partial functions in this fashion, such as a cooler valve with a heating valve. It is also an advantage hereby that such systems are not exclusively reliant on a master control device, because, due to its inherent intelligence, expenditure for data transmission and time are spared.
The microcontroller integrated in the control valve is also capable of processing signals from external sensors. For instance, data from temperature sensors and/or pressure differential sensors can be sent to the microcontroller in a simple fashion by way of control lines, which, once it is evaluated, also act on the position variables to be determined. The control valve can therefore adjust a target temperature and/or a desired flow rate in a branch of flow to a heat exchanger on its own. A self-diagnosis of the control valve is also possible, the result of which can be sent to the first control unit.
In the normal case, the second control unit receives a setpoint for the position of the valve member from the first control unit by way of a signal line. In an embodiment of the invention, the setpoint is input as an analog signal, whereby this must be converted before evaluation in a digital processor using an analog-digital converter. An essential advantage of analog signals is the widespread use of the signal format, so that many instruments can be controlled with it.
In a further embodiment, the setpoint is input as a pulse width signal. This is a digital signal that, on the one hand, is easy to create and, on the other, can be evaluated without conversion. For use in the cooling circuit of an internal combustion engine, the high interference immunity and the simple possibility of detecting and eliminating a malfunction of the control is particularly advantageous. In a further embodiment, the setpoint is available as information via a CAN bus. The control valve is preferably connected to the CAN (Controller Area Network) bus in the motor vehicle for this purpose. Only one connection is required here, since the communication is carried out bidirectionally. This variant is particularly suited to an evaluation of the valve position in thermomanagement.
The setpoint input by the first control unit is compared with a determined actual value in the second control unit, a logical switch, or the microcontroller of the control valve, and processed to a position variable. The invention provides multiple variants for the determination of the actual value. On the one hand, for example, the actual value can be determined by way of a rotary potentiometer that is coupled with a drive axle of the valve member. This type of position detection is very simple. However, due to mechanical contact, it is sensitive to wear. A second variant uses inductive or capacitive displacement measurement, which is considerably more robust than the method mentioned previously. Angle determination can also be carried out in a magnetic fashion using GMR or AMR sensors (Giant Magneto Resistive; Anisotropic Magneto Resistive).
Finally, the actual value can be determined by measuring the light intensity of a light path. A very favorable variant is the incremental position detection of the actual value using a light barrier. Appropriately, the drive motor, a direct-current motor, thereby drives the valve member by way of a gear, whereby a gear wheel or a separate wheel on a drive part has markings that are detected by an optical sensor. The optical signals detected by the sensor form a measure of the motion of the valve member.
In order to obtain a reference point, a reference position must first be determined, on which the subsequent measurements are based. According to the invention, a mechanical stop is provided for this purpose. The optical sensor, which can be designed as a hybrid light barrier or a reflection light barrier, is connected with the second control unit by way of a data line. The signal sequence is detected in this. A certain signal sequence can be assigned to an exact position of the valve member, so that the exact position can be determined from a certain signal sequence.
Advantageously, this measurement is noncontact, so that no wear occurs. It is also very exact, since a self-diagnosis can be performed using simple means. For instance, a calibration procedure can be triggered inherently if optical signals fail to appear in a certain period of time.